This invention relates to methods and apparatus for depositing granules onto a moving substrate. More particularly, this invention relates to methods and apparatus for controlling the flow of granules from a blend drop granule dispenser that supplies granules to be deposited onto the moving substrate.
A common method for the manufacture of asphalt shingles is the production of a continuous strip of asphalt shingle material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphalt strip material, either an organic felt or a glass fiber mat is passed through a coater containing liquid asphalt to form a tacky asphalt coated strip. Subsequently, the hot asphalt strip is passed beneath one or more granule applicators which apply the protective surface granules to portions of the asphalt strip material. Typically, the granules are dispensed from a hopper at a rate which can be controlled by making manual adjustments to the width of the discharge slot of the hopper. In the manufacture of colored shingles, two types of granules are employed. Headlap granules are granules of relatively low cost for portions of the shingle which are to be covered up. Colored granules or prime granules are of relatively higher cost and are applied to the portion of the shingle which will be exposed on the roof.
Not all of the granules applied to the hot, tacky, asphalt coated strip adhere to the strip, and, typically, the strip material is turned around a slate drum to invert the strip and cause the non-adhered granules to drop off. These non-adhered granules, which are known as backfall granules, are usually collected in a backfall hopper. The backfall granules are eventually recycled and discharged onto the sheet.
To provide a color pattern of pleasing appearance the colored shingles are provided in different colors, usually in the form of a background color and a series of granule deposits of different colors or different shades of the background color. These highlighted series of deposits, referred to as blend drops, are typically made by discharging granules from a series of blend drop granule dispensers. To produce the desired effect, the length and spacing of the blend drops must be accurate. The length and spacing of each blend drop on the sheet is dependent on the relative speed of the sheet and the length of time during which the blend drop granules are discharged.
A uniform distribution of blend drop granules on the sheet is also desired. A uniform distribution produces a sharp distinction between the blend drop and the background areas, and this provides a more pleasing appearance to the shingle. Also, a uniform distribution enables the blend drop to be applied with a minimum of excess granules, thereby reducing the amount of wasted prime granules that must be downgraded for use in the headlap area of the shingle. To produce a uniform distribution, a constant flow rate of granules during the discharge from the blend drop dispenser is desired.
One method of applying granules to the moving sheet involves discharging the granules from hoppers using a fluted roll at the hopper discharge slot. The fluted roll is rotated to discharge the blend drop granules onto the asphalt sheet. The roll is ordinarily driven by a drive motor, the roll being positioned in the drive or non-drive position by means of a brake-clutch mechanism. This mechanical action required to discharge the blend drop granules with a fluted roll is burdened with inherent limitations. The distribution of the granules from the fluted roll is very non-uniform, resulting in a general inability to provide sharp lines at the leading edge and trailing edge of the blend drops. Further, the duration of each granule discharge is too long to produce a short blend drop deposit on a sheet traveling at high machine speeds. Also, the discharge of blend drop granules cannot achieve a constant flow rate quickly enough to produce a uniform granule deposit. Consequently, there is a limit to the sharpness of the blend drops on the shingle using a fluted roll.
Another method of applying granules to the moving sheet involves discharging granules from a discharge slot in a linear nozzle, as disclosed in U.S. Pat. No. 5,746,830 to Burton et al. The granules are fed to the nozzle from a hopper. The discharge of granules from the linear nozzle is controlled by regulating the atmospheric pressure above the accumulation of granules in the nozzle. Increased or positive pressure above the granules in the nozzle causes the granules to flow through the discharge slot, and a negative pressure causes the granules to clog the discharge slot, thereby stopping the flow of granules through the slot.
U.S. Pa. No. 6,228,422 to White et al. discloses a granule discharging apparatus in which the flow of granules from a hopper discharge slot is regulated by a slide gate that is arranged to be reciprocated linearly to open and close the discharge slot. The slide gate is operated to change to discharge slot to full open condition every time there is a blend drop. Therefore, there is no mechanism to vary the flow to accommodate changes in the linespeed of the moving sheet.
It is desired to provide an improved method and apparatus for discharging blend drop granules onto the moving sheet to produce a deposit having a uniform distribution of granules. It is particularly desirable to provide a granule depositing system that is more responsive to changes in line speed of the asphalt coated sheet, particularly at the higher line speeds. Also, it would be helpful to have a granule depositing system with more accurate controls of the blend drops to provide increased granule efficiency and improved blend drop appearance. It would also be beneficial to have a blend drop granule dispenser that more accurately opens and closes the granule deposition mechanism in response to changes in line speed.
The above objects as well as other objects not specifically enumerated are achieved by apparatus for depositing granules onto a substrate, where the apparatus includes a hopper for containing granules, the hopper having a discharge slot, and a reciprocating gate mounted for rotation across the slot to open and close the slot.
According to this invention there is also provided apparatus for depositing granules onto a substrate, where the granules have a median diameter. The apparatus includes a hopper for containing granules, the hopper having a discharge slot. A gate is mounted for movement across the slot to open and close the slot. The gate has a leading edge with a thickness that is within the range of from about 0.2 to about 1.5 times the median diameter of the granules.
According to this invention there is also provided apparatus for depositing granules onto a substrate, the granules having a median diameter. The apparatus includes a hopper for containing granules, the hopper having a discharge slot having a width. An elongated gate is mounted for movement across the slot to open and close the slot. The gate has a leading edge and a shank portion extending back from the leading edge for a distance of at least the width of the slot, wherein the thickness of the shank portion is less than about 400 mils.
According to this invention there is also provided a method of depositing granules onto a moving substrate. The method includes providing a hopper for containing granules, where the hopper has a discharge slot. A gate is moved across the slot to open and close the slot. When the slot is open granules fall from the hopper, and when the slot is closed granules are prevented from falling from the hopper. The method further includes detecting the speed of the substrate, and controlling the extent of opening of the slot by the gate to meter the granules falling from the hopper in response to the speed of the substrate.
According to this invention there is also provided a method of depositing granules onto a moving substrate. The method includes providing a hopper for containing granules, where the hopper has a discharge slot, and moving a gate across the slot to open and close the slot. When the slot is open granules fall from the hopper, and when the slot is closed granules are prevented from falling from the hopper. The method includes controlling the speed of the movement of the gate, and independently controlling the extent of opening of the slot by the gate to meter the granules falling from the hopper.
According to this invention there is also provided a method of depositing granules onto a moving substrate. The method includes providing a hopper for containing granules, the hopper having a discharge slot, and moving a gate across the slot to open and close the slot. When the slot is open granules fall from the hopper, and when the slot is closed granules are prevented from falling from the hopper. The method further includes controlling the acceleration rate of the gate during the opening of the slot so that the acceleration rate does not exceed about 3 g.
According to this invention there is also provided a method of depositing granules onto a moving substrate. The method includes providing a hopper for containing granules, the hopper having a discharge slot, and moving a gate across the slot to open and close the slot. When the slot is open granules fall from the hopper, and when the slot is closed granules are prevented from falling from the hopper. The method further includes controlling the acceleration of the gate during the opening of the slot so that the acceleration rate is positive during a first portion of the opening of the slot, and the acceleration rate is approximately zero during a second portion of the opening of the slot.
According to this invention there is also provided a method of depositing granules onto a moving substrate. The method includes providing a hopper for containing granules, the hopper having a discharge slot, and moving a gate across the slot to open and close the slot. When the slot is open granules fall from the hopper, and when the slot is closed granules are prevented from falling from the hopper. The method further includes controlling the velocity of the gate during the closing of the slot so that the velocity does not exceed about 130 ft./min.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.